test(lighthouse-react): Use static imports gated by MODE for tree-shaking

[mydea]

Summary

Replace the dynamic await import('./sentry/<mode>') branching in main.tsx with a single static import * as Sentry from '@sentry/react' guarded by import.meta.env.MODE. This more closely mirrors what a real consumer app looks like: a static SDK import at the top, with Sentry.init() called conditionally. The build matrix still produces three distinct bundles via vite build --mode <mode>, but the code path is now realistic instead of a code-splitting trick.

How tree-shaking handles each mode

Vite inlines import.meta.env.MODE as a string literal at build time. Rollup then eliminates dead if branches, and @sentry/react's "sideEffects": false lets the namespace import be tree-shaken away entirely when no member is referenced.

• no-sentry: both branches are statically dead → Sentry.* unreferenced → the entire @sentry/react import is dropped from the bundle.
• init-only: only Sentry.init({ enabled: false }) survives; browserTracingIntegration / replayIntegration are tree-shaken.
• tracing-replay: full SDK + tracing + replay.

Verified bundle output

Mode	Bundle	Sentry SDK symbols¹
no-sentry	144 KB	0
init-only	229 KB (+85 KB)	present
tracing-replay	418 KB (+274 KB)	7

¹ Count of captureException / startSpan / getCurrentScope / __SENTRY__ / sentry-trace occurrences in the output JS. The only Sentry literal in the no-sentry bundle is the marketing copy string in App.tsx, not SDK code.

The per-mode helper files in src/sentry/ are no longer needed and have been deleted.